For example, a fuel cell system mounted to a vehicle such as an automobile as a drive source comprises a fuel cell that generates electricity through an electrochemical reaction between a fuel gas including hydrogen gas and an oxidation gas. The fuel cell has a stack structure in which a plurality of cells is laminated.
During an operation of the fuel cell system, for example, a portion of water produced by an electrochemical reaction in the fuel cell stack penetrates into a cell. When a water content in the cell increases excessively and the cell becomes clogged by water, there may be cases where gas is unable to travel through the cell and a gas supply deviates from stoichiometry, resulting in a decrease in generated voltage.
Therefore, clogging of water in a cell of a fuel cell stack is detected and the detected water in the cell is discharged by increasing a purge volume (refer to Patent Document 1).
Patent document 1: Patent Publication JP-A-2002-260704
Patent document 2: Patent Publication JP-A-2005-63712
Patent document 3: Patent Publication JP-A-2007-184136
Patent document 4: Patent Publication JP-A-2003-217624
However, there may be cases where simply increasing a purge volume as described above does not restore generated voltage. This is conceivably due to the fact that purging and reducing water content may result in a greater variation in cell pressure loss among cells in a fuel cell stack, in which case gas is not sufficiently supplied to a cell with a greatest relative pressure loss and electricity is not generated efficiently.